STUDIES  CONCERNING  THE  ESSENTIAL 
NATURE  OF  ALUMINUM  AND  SILICON 
FOR  PLANT  GROWTH 


by  #£MM£t^ 

ANNA  L.  SOMMER 


University  of  California  Publications  in  Agricultural  Sciences 
Volume  5,  No.  2,  pp.  57-81,  2  figures  in  text 


uwvmsrnr  of  caufqrn** 
LiBRAR 

COLLEGE  Of  AG*CUUUKE 


UNIVERSITY  OF  CALIFORNIA  PRESS 

BERKELEY,  CALIFORNIA 

1926 


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2.  Studies  Concerning  the  Essential  Nature  of  Aluminum  and  Silicon  for 
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1926   30 

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STUDIES  CONCERNING  THE  ESSENTIAL  NATURE 

OF  ALUMINUM  AND  SILICON  FOR 

PLANT  GROWTH 


BY 
ANNA  L.  SOMMER 


University  of  California  Publications  in  Agricultural  Sciences 

Volume  5,  No.  2,  pp.  57-81,  2  figures  in  text 

Issued  May  6,  1926 


University  of  California  Press 
Berkeley,  California 


Cambridge  University  Press 
London,  England 


STUDIES   CONCERNING   THE 

ESSENTIAL  NATURE  OF  ALUMINUM  AND 

SILICON  FOR  PLANT  GROWTH 


BY 

ANNA  L.  SOMMEE 


INTRODUCTION* 

One  of  the  first  problems  to  occupy  the  attention  of  the  plant 
physiologist  was  the  determination  of  the  essential  nature  of  elements 
supplied  by  the  soil.  The  question  appeared  to  be  answered  about  the 
middle  of  the  last  century  by  Knop,  who  demonstrated  that  plants 
grew  well  in  a  dilute  solution  of  KN03,  MgS04,  KH2P04,  and  CaS04, 
to  which  a  trace  of  FeP04  had  been  added.  Until  recently,  however, 
investigators  have  failed  to  consider  the  fact  that  possible  essential 
elements  might  be  introduced  as  impurities.  Since  some  elements  are 
required  only  in  very  small  amounts,  experiments  to  ascertain  whether 
or  not  they  are  essential  can  be  conducted  successfully  only  when 
purified  salts  are  employed.  It  is  therefore  not  surprising  that  nega- 
tive results  have  followed  the  few  investigations  of  other  elements 
than  those  named  by  Knop. 

Among  these  investigations  are  those  of  Maze,s  McHargue,9  and 
Warington.17  Maze  was  the  first  to  use  purified  salts  and  reported 
marked  improvement  in  growth  when  he  added  aluminum,  boron, 
fluorin,  and  iodine  to  solution  cultures  in  which  maize  was  grown. 
McHargue  proved  manganese  to  be  essential  to  all  plants  with  which 
he  worked ;  these  including  beans,  wheat,  spinach,  and  radishes. 
Warington  found  that,  although  boron  may  not  be  essential  for  all 
plants,  it  is  essential  for  certain  of  the  legumes. 

All  plants  in  their  natural  environment  absorb  aluminum  and 
silicon,  and  the  studies  reported  in  this  paper  were  conducted  to  get 
additional  evidence  concerning  the  essential  nature  of  these  elements, 
as  very  little  has  been  done  under  sufficiently  controlled  conditions  or 
including  a  large  enough  number  of  plants  to  prove  that  these  elements 
were  actually  essential. 


*  The  writer  wishes  to  acknowledge  her  indebtedness  to  Frofessor  C.  B. 
Lipman  for  helpful  counsel  during  the  course  of  these  investigations;  the 
investigation  concerning  silicon  was  suggested  by  him. 


58  University  of  California  Publications   in  Agricultural  Sciences      [Vol.5 

Since  silicon  and  aluminiim  are  present  in  the  soil  in  such  large 
amounts  and  are  absorbed  by  the  plant,  further  studies  as  to  whether 
or  not  these  elements  are  essential  are  important. 

There  is  sufficient  evidence  to  show  that  aluminum  is  toxic  at  low 
concentrations  to  higher  plants.  Miyake11  and  Mirasol10  have  shown 
that  the  aluminum  ion  is  more  toxic  than  the  hydrogen  ion  of  the 
same  concentration.  Ruprecht,13  on  investigating  infertility  of  soils 
after  continued  use  of  (NH4)2  S04,  found  an  increase  in  soluble 
aluminum.  In  experiments  with  peas  in  culture  solutions  he  found 
21.6  p. p.m.  (the  lowest  concentration  used)  to  be  toxic.  Kratzman5 
reported  aluminum  salt  toxic  to  a  number  of  higher  plants  at  a  con- 
centration of  .005  per  cent,  and  slightly  stimulating  at  .0001  per  cent. 
In  a  preliminary  experiment  reported  in  the  same  paper,  this  investi- 
gator found  8  p. p.m.  to  be  very  toxic  to  wheat,  and  some  depression  in 
growth  at  2  p. p.m.  Abbot,  Connor  and  Smalley1  found  the  toxicity 
of  certain  soils  to  be  caused  by  soluble  aluminum  salts,  while  Hartwell 
and  Pember3  were  able  to  explain  why  certain  acid  soils  were  more 
toxic  to  barley  than  to  rye  by  showing  that  barley  is  particularly 
sensitive  to  aluminum. 

Aluminum  was  one  of  the  elements  which  Maze8  found  necessary 
for  the  normal  development  of  maize.  The  salts  he  used  were  highly 
purified  and  his  results  indicate  that  fluorine,  iodine,  and  especially 
boron  are  also  necessary.  Maze,  however,  used  only  a  small  number  of 
plants  in  each  of  three  experiments  and  marked  irregularities  occur 
in  some  of  his  data.  Further  investigations  of  a  similar  nature  are 
therefore  necessray  before  definite  conclusions  can  be  drawn  concern- 
ing the  essential  nature  of  these  elements  for  maize.  This  criticism 
does  not  hold  for  boron,  for  in  all  cases  marked  depression  was  evident 
if  boron  was  lacking. 

Although  Stoklasa10  used  so  far  as  we  know  only  the  so-called 
chemically  pure  salts,  he  obtained  striking  improvements  in  growth 
when  he  added  aluminum  to  solution  and  silica  jelly  cultures  in  which 
he  grew  certain  hydrophytes.  J  uncus  effusus  in  solution  culture  with- 
out aluminum  died  in  from  56  to  69  days,  and  Glyceria  aquatica  in 
silica  jelly  cultures  died  in  22  days.  Other  hydrophytes,  although 
they  did  not  die  in  the  solution  without  aluminum,  showed  remarkable 
improvement  in  growth  when  it  was  added.  He  also  found  that 
aluminum  stimulated  the  growth  of  mesophytes  such  as  Hordeum 
distichum,  Triticum  vulgare,  and  arena  satica,  but  that  xerophytes, 
including  Attosurus  crispus,  Polygonatum  officinale,  and  Iris  bohemica 


1926]  Sommer:   Aluminum  and  Silicon  for  Plant   Growth  59 

were  not  affected  by  the  addition  of  13.5  p. p.m.  or  20  p. p.m.  aluminum 
to  the  solution  cultures  in  which  they  were  grown  but  were  injured 
by  27  p.p.m.  However,  since  he  added  0.5  grams  Ca3(P04),  to  the 
solutions  and  aerated  daily,  the  amounts  in  solution  are  probably  not 
represented  by  the  amounts  added.  Judging  from  the  results  of  other 
investigators  (Ruprecht13),  Abbot,  Connor  and  Smalley,1  Hartwell 
and  Pember,3  and  the  writer,  even  the  smallest  amount  added  would 
have  been  toxic  to  mesophytes  and  xerophytes  if  not  to  hydrophytes 
had  it  remained  in  solution.  Stoklasa  attributes  the  difference  in  the 
requirements  for  aluminum  of  these  three  groups  of  plants  to  the 
difference  in  the  amounts  to  which  they  have  become  accustomed, 
owing  to  their  environments. 

The  earliest  ideas  regarding  the  role  of  silicon  in  plant  growth 
were  based  upon  speculation.  Sir  Humphrey  Davy2  in  his  book,  "The 
Elements  of  Agricultural  Chemistry"  (1814),  stated,  "The  siliceous 
epidermis  of  plants  serves  as  a  support,  protects  the  bark  from  the 
action  of  insects  and  seems  to  perform  a  part  in  the  economy  of  these 
feeble  vegetable  tribes  (Grasses  and  Equisetales)  similar  to  that  per- 
formed in  the  animal  kingdom  by  the  shell  of  crustaceous  insects." 
Liebig  attributed  the  rigidity  of  the  stalks  of  cereals  to  potassium 
silicate  and  explained  the  lodging  of  wheat  by  assuming  a  deficiency 
of  silicon.  Pierre,12  on  the  other  hand,  claimed  to  have  evidence  that, 
other  things  being  equal,  wheat  with  the  highest  silicon  content  was 
most  likely  to  lodge,  and  agreed  with  Sachs13  that  it  was  lignification 
of  tissues,  favored  by  air,  light,  and  the  absence  of  too  much  water, 
which  prevented  lodging.  The  opinions  of  later  investigators  are  just 
as  contradictory. 

Jodin4  was  one  of  the  first  to  make  a  special  attempt  to  determine 
whether  or  not  silicon  is  essential  to  plant  growth.  Like  other  investi- 
gators, he  grew  his  plants  in  glass  containers  and  made  no  attempt 
to  purify  the  salts  used  for  the  solutions.  He  grew  four  generations 
of  plants.  The  plants  grew  well,  but  the  fourth  generation  produced 
no  seed.  This  he  thought  was  accidental  and  concluded  that  silicon  is 
probably  not  essential.  No  conclusion,  however,  can  be  drawn,  since 
his  plants  were  not  really  grown  in  the  absence  of  silicon  and  he  had 
no  control  plants  to  show  any  beneficial  effects  which  might  have  been 
obtained  with  a  larger  amount  of  silicon.  An  analysis  of  his  second 
generation  plants  showed  0.2  per  cent  of  the  dry  weight  to  be  Si03 
(reported  as  such  by  the  author). 


60  University  of  California  Publications  in  Agricultural  Sciences      [Vol.  5 

Working  a  little  later  (1883)  with  only  one  generation  of  plants, 
Kreuzhage  and  Wolff6  carried  on  expeirments  with  oats  in  solution 
cultures,  and  usually,  though  not  always,  obtained  an  increase  in  dry 
weight  when  H2SiOa  was  added.  The  increase  in  grain  was,  however, 
marked  and  consistent.    They  used  uncoated  glass  containers. 

Sprecher15  also  worked  with  oats  in  solution  cultures.  He  used 
three  types  of  solutions  and  varied  the  conditions  as  follows :  solutions 
without  HoSiOs  in  jars  coated  with  paraffin,  solutions  without  H2SiO:i 
in  uncoated  glass  containers,  and  solutions  with  H2Si03  in  uncoated 
glass  containers.  He  obtained  marked  increases  with  H2SiOa  and 
although  he  does  not  say  that  silicon  is  essential  he  considers  it 
very  important  in  plant  metabolism.  The  plants  in  paraffined  jars 
had  very  stunted  root  systems,  but  the  total  dry  weight  was  about 
the  same  as  that  for  plants  without  H2Si03  in  uncoated  jars.  He  sug- 
gests that  the  glass  may  have  a  stimulating  effect  on  root  development 
but  makes  no  mention  of  the  toxic  effect  of  paraffin.  The  analyses  of 
his  plants  showed  more  silicon  than  could  be  accounted  for  by  that 
found  in  the  seed  so  that  in  his  work,  as  in  the  work  of  earlier 
investigators,  silicon  was  not  entirely  eliminated. 


TECHNIQUE  OF  THE  PRESENT  EXPERIMENTS 

All  plants  employed  in  these  experiments  were  grown  in  solution 
cultures  in  glass  jars.  In  most  of  the  experiments  one-quart  or  two- 
quart  mason  jars  were  employed,  paraffined  corks  being  utilized  as 
supports  for  the  plants.  In  two  cases  large  glass  containers  of  16- 
liter  capacity  were  used,  these  being  made  by  cutting  the  tops  off  of 
5-gallon  carboys.  Wooden  covers  were  made  for  the  large  containers — 
twenty-four  holes  being  bored  in  each  and  the  board  thoroughly 
impregnated  with  hot  paraffin. 

In  order  to  prevent  traces  of  the  elements  in  question  from  being 
dissolved  out  of  the  glass,  the  containers  were  coated  for  the  first  series 
with  paraffin,  and  for  the  succeeding  series  with  Valspar,  a  resistant 
varnish.  A  coat  of  Valspar  was  applied  and  allowed  to  dry  over  night, 
the  container  then  being  baked  for  half  an  hour  at  110°  to  140°  C. 
Two  coats  of  Valspar  were  applied  in  this  manner. 

In  order  to  dissolve  out,  as  far  as  possible,  the  soluble  matter  from 
the  Valspar,  the  containers  were  filled  with  distilled  water,  to  which 
20  c.c.  concentrated  HC1  had  been  added,  and  were  allowed  to  stand 


1926]  Sommer:  Aluminum  and  Silicon  for  Plant  Growth  61 

for  two  days.  This  dilute  solution  of  acid  was  then  removed,  the  jars 
rinsed,  filled  with  distilled  water,  and  kept  filled  for  a  period  of  ten 
days.    The  water  was  changed  every  other  day. 

Redistilled  water  was  used  in  making  up  the  solutions  and  its  only 
contact  with  glass  was  while  it  was  being  collected  in  pyrex  glass  con- 
tainers. The  salts  used  in  making  up  the  solutions  were  tested  for 
the  elements  to  be  eliminated. 

The  alizarin  test  was  used  for  aluminum  and  was  found  very  sensi- 
tive (one  part  in  ten  million)  in  the  absence  of  interfering  ions.  When 
traces  of  aluminum  were  found,  the  salts  were  either  purified  or  made 
up  from  the  elements  or  from  compounds  containing  no  aluminum. 
Attempts  to  purify  KH2P04  by  recrystalization  were  unsuccessful, 
but  H3P04  and  K2C03,  aluminum  free,  were  obtained  and  the  salt 
prepared  from  them.  For  the  first  series  magnesium  was  supplied  in 
the  form  of  Mg(N03)2  made  from  the  metal  and  redistilled  HN03. 
CaS04  was  purified  by  washing,  first  with  H,S04  and  then  with  redis- 
tilled water.  KN03  was  obtained  which  gave  no  test  for  aluminum. 
Since  the  nitrate  ion  interferes  with  the  alizarin  test,  it  was  first 
decomposed. 

In  the  silicon  series  CaS04,  KN03,  and  MgHP04  were  used.  The 
CaS04  was  prepared  from  CaCL  and  H2S04,  and,  since  separating 
Si02  entirely  from  CaS04  as  such  would  be  very  difficult,  HC1  was 
added  to  a  solution  of  CaCl,  to  precipitate  the  silicon  as  H2Si03.  The 
solution  was  then  evaporated  to  dryness  and  heated  for  half  an  hour 
at  120°  C.  The  residue  was  dissolved  and  filtered.  This  process  was 
repeated  several  times  and  the  CaS04  was  then  precipitated  from  the 
CaCl2  solution  with  H2S04.  The  CaS04  was  washed  free  from  acid 
with  redistilled  water.  KN03  was  purified  by  evaporating  the  solu- 
tion to  dryness  in  the  presence  of  HN03,  heating  at  120°  C.  for  half 
an  hour,  redissolving,  and  filtering.  This  process  was  repeated  several 
times  and  the  salt  was  then  recrystallized.  The  MgHP04  was  found 
to  contain  only  0.2  milligram  Si02  per  10  grams  of  the  salt.  The  only 
attempt  to  purify  it  was  by  trying  to  dissolve  out  the  silicon  com- 
pounds. This  was  done  by  agitating  100  grams  of  MgHP04  for  eight 
hours  in  a  20-liter,  Valspar-coated  bottle.  The  first  solution  was  dis- 
carded, the  second  was  used  in  making  up  the  culture  solutions  to 
which  silicon  was  added,  and  the  final  was  used  for  the  silicon-free 

4 

solutions.  It  was  hoped  in  this  way  to  eliminate  most  of  the  silicon ; 
other  methods  of  purifying  this  salt  seemed  less  satisfactory. 


62  University  of  California  Publications  in  Agricultural  Sciences      [Vol.  5 

With  the  exception  of  Maze  (working  with  aluminum),  no  investi- 
gator in  testing  the  essential  nature  of  aluminum  or  silicon  made  any 
effort  to  exclude  dust.  Since  these  elements  are  omnipresent  and  are 
the  principal  constituents  of  dust,  it  would  seem  necessary  to  exclude 
the  latter  in  such  experiments.  To  minimize  contamination  from  this 
source,  all  plants,  excepting  those  of  the  first  series  (wheat,  grown 
out  of  doors),  were  grown  in  glass  chambers  in  the  greenhouse.  These 
chambers  were  four  feet  high,  three  feet  wide,  and  long  enough  to 
accommodate  the  number  of  jars  in  a  series.  The  glass  extended 
upward  from  a  point  just  below  the  tops  of  the  containers,  a  small 
space  near  the  top  being  left  unenclosed  for  ventilation. 

The  positions  of  the  individual  containers  were  frequently  inter- 
changed within  the  chamber  in  order  to  equalize  the  amount  of  light 
received. 


EXPERIMENTAL  ALUMINUM  SERIES 

Wheat  was  used  in  the  first  experiment  in  which  the  effect  of 
aluminum  on  plant  growth  was  studied.  The  seeds  were  germinated 
in  the  usual  way  on  paraffined  mosquito  netting.  When  the  seedlings 
were  a  week  old,  the  remains  of  the  old  seeds  were  removed  and  the 
plants  transferred  to  the  solutions  to  be  tested. 

The  salts  used  for  the  culture  solutions  in  this  experiment  were 
chosen  because  they  were  the  first  group  containing  the  necessary 
elements  which  the  writer  obtained  free  from  aluminum.  The  com- 
position of  the  solution  was  as  follows : 

Gm.  per  1 

KN03  338 

CaS04    500 

Mg(N03),6H20    400 

KH2P04  150 

FeSO,  Trace 

There  were  six  groups  of  plants  in  each  series.  The  plants  were 
grown  in  the  following  solutions : 

*  Aluminum  added 
Solution  p. p.m.  Remarks 

(a)   Culture  solution  0  Purified  salts 

(6)    Culture  solution  2  Purified  salts 

(c)  Culture  solution  4  Purified  salts 

(d)  Culture  solution  6  Purified  salts 
(c)  Culture  solution  8  Purified  salts 
(/)   Culture  solution  0  Unpurified  salts 

*  Aluminum  was  added   in  the  form  of  aluminum   sulphate. 


1926]  Sommer:  Aluminum  and  Silicon  for  Plant  Growth  63 

The  unpurified  salts  used  were  the  so-called  "chemically  pure" 
salts.  Each  group  consisted  of  five  cultures  of  four  plants  each.  The 
containers  were  one-quart  mason  jars.  The  plants  were  grown  out  of 
doors  in  a  place  fairly  well  protected  from  wind. 

OBSERVATIONS 

April  8.  Plants  in  unpurified  salts  were  tillering  well.  Those  in  solutions  of 
purified  salts  with  and  without  aluminum  were  much  smaller.  These, 
especially  the  ones  with  8  p. p.m.  aluminum  showed  depression  in  root 
growth  and  top  development. 

April  15.  Plants  in  solutions  of  unpurified  salts  were  much  the  best.  Plants 
in  solutions  of  purified  salts  with  the  addition  of  2  p. p.m.  aluminum  had 
better  tops  and  longer  roots  than  those  without  aluminum.  All  plants 
in  solutions  containing  more  than  2  p. p.m.  of  aluminum  were  smaller 
than  those  in  solutions  containing  none. 

April  23.  A  rather  strong  wind  carrying  a  great  deal  of  dust  occurred. 

April  30.  Solutions  changed.  All  plants  in  solutions  of  purified  salts  with  no 
aluminum,  and  some  of  those  in  solutions  with  2  p. p.m.  aluminum,  were 
beginning  to  tiller.  Tops  and  roots  of  all  plants  were  making  better 
growth.  There  was  less  difference  between  the  size  of  the  tops  of  the 
plants  containing  8  p. p.m.  aluminum  and  those  of  the  other  groups  than 
there  had  been. 

Roots  of  plants  in  solutions  containing  2  and  4  p.p.m.  aluminum  were 
longer  and  more  branched  than  those  in  solutions  of  purified  salts  without 
aluminum. 

May  5.  Plants  in  solutions  without  aluminum  were  making  rapid  growth. 

May  22.  Plants  harvested. 

Plants  in  solutions  with  no  aluminum  were  well  tillered  and  nearly 
as  good  as  those  in  solutions  of  unpurified  salts. 

2  p.p.m.  aluminum.  Some  plants  had  as  many  as  three  tillers;  some 
had  only  a  single  stalk. 

4  p.p.m.  Plants  were  very  variable;  some  were  very  small  while  others 
had  a  few  tillers  and  good  root  systems. 

6  p.p.m.  Stalks  were  thick,  had  few  tillers  and  root  systems  were 
greatly  depressed. 

8  p.p.m.    All  plants  had  very  small  tops  and  short  roots. 

There  was  a  marked  difference  in  the  growth  of  the  plants  in  the 
group  with  purified  salts  without  aluminum  after  the  wind  storm. 
Since  this  was  probably  due  to  contamination  by  dust,  none  of  the 
plants  were  weighed. 

Although  this  series  was  not  conclusive  as  to  whether  or  not 
aluminum  is  essential  to  plant  growth,  it  showed  the  toxicity  of 
aluminum  and  indicated  that  2  p.p.m.  is  too  large  an  amount  to  be 
added  to  cultures  of  wheat  where  a  stimulating  effect  is  desired. 


C4  University  of  California  Publications  in  Agricultural  Sciences      [Vol.  5 


Aluminum  Series  with  Peas 

The  type  of  solution  used  was  the  same  as  that  in  the  preceding 
experiment  except  that  2  p.p.m.  manganese  in  the  form  of  MnS04 
was  added. 

Since  2  p.p.m.  aluminum  had  been  found  to  depress  the  growth  of 
wheat,  1  p.p.m.  was  the  highest  concentration  used  in  this  series.  The 
solutions  employed  were  as  follows: 


Solution 

Al 

Liminum  added 
p.p.m. 

Remarks 

(a) 

Culture  solution 

0 

Purified  salts 

(») 

Culture  solution 

I 

Purified  salts 

(<0 

Culture  solution 

1 

Purified  salts 

(d) 

Culture  solution 

0 

Unpurified  salts 

There  were  eight  cultures  with  four  plants  per  culture  to  each 
group.  The  containers  were  one-quart  mason  jars.  The  seed  was 
germinated  on  paraffined  mosquito  netting  and  the  cotyledons  removed 
before  the  plants  were  transferred  to  the  culture  solutions  on 
August  23. 

OBSERVATIONS 

September  6.  The  plants  in  solutions  of  purified  salts  without  aluminum  were 
beginning  to  bloom  and  appeared  smaller  than  the  others. 

September  10.  Plants  in  series  with  aluminum  and  with  unpurified  salts  were 
beginning  to  bloom. 

September  28.  Solutions  changed. 

October  18.  Plants  harvested. 

All  plants  except  four,  in  the  solutions  of  purified  salts  without 
aluminum,  had  reached  maturity  and  stopped  growing.  These  four  had 
gone  through  the  cycle  of  growth  and  then  sent  out  new  growth  and 
produced  another  lot  of  flowers.  These  plants  weighed  more  than  the 
others  in  this  group. 

The  average  weight  per  plant  and  the  average  weight  of  seed  per 
plant  are  given  in  table  1. 

Although  there  was  no  gain  in  the  total  dry  weight  with  |i  p.p.m. 
aluminum,  there  seems  to  be  a  slight  gain  in  the  weight  of  the  seed. 
With  1  p.p.m.  aluminum  there  was  a  noticeable  gain  in  both  seed  and 
dry  weight.  The  plants  grown  in  solutions  of  unpurified  salts  were 
the  best. 

Nearly  all  work  concerning  the  essential  nature  of  elements  has 
been  done  with  seed  from  plants  which  have  been  grown  in  the  presence 
of  the  clement  in  question,  the  work  of  Jodin  already  cited  being  an 
exception.    It  seems  not  unlikely  that,  when  an  element  is  needed  in  a 


1926]  Sommcr:  Aluminum  and  Silicon  for  Plant  Growth  65 

very  small  quantity,  the  seed  may  contain  enough  to  allow  fair  if  not 
normal  growth  of  the  plant  when  this  element  is  lacking  in  the  solu- 
tion. The  second  generation,  however,  should  show  the  need  of  this 
element  to  a  much  greater  extent,  and  it  was  therefore  decided  to  use 
seed  grown  with  and  without  aluminum  for  second-generation  work. 
Seed  of  the  plants  grown  in  solutions  (1)  of  purified  salts  with  no 
aluminum,  and  (2)  with  1  p. p.m.  aluminum,  and  (3)  of  unpurified 
salts  were  germinated.  The  seed  in  all  cases  germinated  well,  but  the 
seedlings  from  seed  of  plants  grown  in  purified  salts  without  aluminum 
were  smaller  than  those  of  the  two  other  groups. 

TABLE  1 

Dry  Weight  of  Pea  Plants  and  Seed  Grown  in  Solutions  of  Purified  Salts 
With  and  Without  Aluminum  and  in  Solutions  of  Unpurified  Salts 

Average  total  Average  weight 

dry  weight  of  seed  per 

Number  of                        per  plant  plant  in 

Treatment                                   plants                              in  grams  grams 

No  aluminum  32  .49  ±  .02  .22  ±  .01 

Aluminum  *  p.p.m 32  .48  ±  .01  .25  ±  .01 

Aluminum  1  p.p.m 32  .55  ±  .02  .28  ±  .01 

Unpurified  salts  32  .59  ±  .02  .31  ±  .01 

After  the  plants  were  transferred  to  the  culture  jars  in  the  green- 
house, the  roots  of  the  plants  of  both  groups  in  the  solutions  of  purified 
salts  became  infected  by  fungi  and  died.  Those  in  solutions  of 
unpurified  salts  were  not  noticeably  attacked. 


Aluminum  Series  with  Millet 

Since  work  with  silicon  was  being  carried  out  at  the  same  time, 
groups  of  plants  with  silicon  and  aluminum  and  with  silicon  alone 
were  included  in  this  series.  The  salts,  however,  were  purified  in 
respect  to  aluminum  only. 

Golden  millet  was  the  variety  used  in  this  experiment. 

A  lot  of  especially  purified  salts  including  MgS04  aluminum  free 
(as  shown  by  analyses)  was  obtained  from  J.  G.  Baker  &  Co.,  and 
magnesium  was  therefore  supplied  in  the  form  of  MgS04. 

The  composition  of  the  solution  was  as  follows: 

Gm.  per  1 

KN03  800 

Kh2P04    150 

MgSO,.7H20  500 

CaS04 46 

MnS04.2H20  0068 

FeS04  Trace 


66  University  of  California  Publications  in  Agricultural  Sciences      [Vol.  5 

Two-quart  mason  jars  were  used.  Twenty-foxir  cultures  of  four 
plants  each  were  set  up  in  the  following  solutions : 

Solution  .  Treatment  Remarks 

(a)  Culture  solution  Nothing  added  Purified  salts 

(b)  Culture  solution  Aluminum  1  p. p.m.  Purified  salts 

(c)  Culture  solution  Aluminum  1  p.p.m.  and  HJ3i03        Purified  salts 

(d)  Culture  solution  H:Si03  Purified  salts 

The  HoSi03  was  prepared  by  precipitation  from  Na.SiOg  with 
H2S04.  The  gel  was  washed  until  the  washings  gave  no  test  for 
sulphate  ion. 

The  seed  was  germinated  on  cheesecloth  and  the  seedlings  trans- 
ferred to  the  culture  solutions  on  August  6. 


OBSERVATIONS 

September  10.  All  plants  were  making  good  growth.  Those  without  Al  or  Si 
appeared  smaller  than  those  of  the  other  groups. 

September  17.  First  heads  (2)  appeared  of  the  group  with  Al. 

September  21.  First  heads  (2)  of  group  with  both  Al  and  Si.    Al  group  8  heads. 

September  29.  Al  group  15  heads,  Al  and  Si  group  6  heads,  Si  group  2  heads. 
Most  of  the  plants  in  the  group  with  both  Al  and  Si  were  turning  yellow. 
The  roots  were  infected  by  fungi. 

October  3.  First  head  appeared  in  the  group  without  Si  or  Al.  Al  group  24 
heads,  Al  and  Si  17  heads,  Si  11  heads.  Most  plants  of  the  Al  and  Si 
group  were  quite  yellow.  The  plants  of  the  group  without  Al  or  Si  were 
producing  new  leaves  at  the  base  which  grew  very  little,  giving  the 
plants  a  tufted  appearance. 

October  15.  Leaves  of  a  number  of  plants  of  the  groups  with  Al  and  Si  were 
quite  yellow.    The  roots  appeared  to  be  infected  by  fungi. 

October  20.  A  number  of  plants  of  the  group  without  Al  or  Si  appeared  to  be 
dying.  Their  roots  were  in  poor  condition.  More  plants  of  the  other 
groups  were  infected  by  fungi,  and  a  number  of  plants  had  died. 

November  6.  Cultures  were  harvested  where  all  plants  were  dead  or  nearly 
dead. 

Number  of  plants  harvested. 

Al  and  Si  group  68  Si  group  24 

No  Al  or  Si  group  20  Al  group  20 

November  30.  Remaining  cultures  were  harvested. 
Total  number  of  plants  dead  from  fungi: 

Al  and  Si  group  74  Si  group  46 

No  Al  or  Si  group  37  Al  group  42 

The  roots  in  most  cases  were  matted  together,  and  were  therefore 
weighed  per  culture  (groups  of  four)  and  averaged.  The  average  weights 
of  roots  and  tops,  the  average  length  of  the  tops,  and  the  total  weight 
of  heads  and  of  seed  are  given  in  table  2. 


1926]  Sommer:  Aluminum  and  Silicon  for  Plant  Growth  67 

Since  the  plants  of  the  group  without  aluminum  and  silicon  were 
least  affected  by  fungi,  the  differences  shown  are  minimum  differences. 
The  plants  of  the  group  with  both  aluminum  and  silicon  were  so  badly 
injured  that  they  could  not  be  considered.  In  the  earlier  stages  of 
growth,  however,  they  did  much  better  than  plants  grown  without 
silicon  and  aluminum. 

TABLE  2 

Description  of  Millet  Plants  Grown  in  Solutions  of  Purified  Salts  With 
and  Without  Aluminum  and  Silicon 

No  Al  or  Si  Al  Si  Al  and  Si* 

Average   dry  weight   of  roots,   gms.            .11  .14  .13                .10 

Average  dry  weight  of  tops,  grams     .41  ±  .08  .57  ±  .11  .62  ±  .10  .49  ±  .07 

Average  length  of  top  in  em 25  ±  7  41  ±  .02  34  ±  9  33  ±  6 

Total  weight  of  heads  in  grams 2.64  11.50  4.50             3.10 

Total  weight  of  seeds  in  grams 23  4.98  .40               .25 

*  Plants   badly   affected   by   fungi. 

Although  the  aluminum  and  silicon  groups  were  in  every  way 
better  than  the  group  without  silicon  and  aluminum,  the  most  striking 
difference  was  shown  by  the  seed.  The  weight  of  seed  from  the  group 
with  silicon  was  nearly  twice,  and  that  from  the  group  with  aluminum 
21.6  times,  as  large  as  that  of  the  group  without  silicon  or  aluminum. 
Moreover,  0.174  grams  of  the  seed  from  the  series  without  aluminum 
or  silicon  came  from  one  culture,  while  the  other  24  cultures  produced 
only  0.054  grams. 


Second  Generation  Aluminum  Series 

In  this  series,  seeds  of  plants  grown  in  the  preceding  experiment 
with  and  without  aluminum  were  used  to  grow  a  second  generation 
in  order  to  learn  the  effect  of  the  absence  of  aluminum.  All  the  seeds 
from  the  group  without  aluminum  or  silicon,  and  an  equal  number 
from  the  group  with  aluminum,  were  taken  for  germination.  The 
seed  from  the  large  culture  of  the  group  without  aluminum  or  silicon 
was  kept  separate  from  that  of  the  rest  of  the  group.  The  total  num- 
ber of  seeds  used  from  each  group  was  90.  In  the  case  of  those  with- 
out aluminum  there  were  64  seeds  from  the  large  culture,  and  26  from 
the  other  24  cultures.  The  percentage  germination  for  the  former 
was  90.6  per  cent,  and  for  the  latter  65.5  per  cent.  All  seed  from 
cultures  with  aluminum  germinated.  The  seedlings  of  the  aluminum 
group  were  vigorous  and  uniform  in  size ;  those  of  the  group  without 
aluminum  were  quite  variable.    The  seedlings  are  shown  in  figure  1. 


68  University  of  California  Publications  in  Agricultural  Sciences      [Vol.  5 

The  seeds  were  germinated  on  netting  coated  with  Valspar ;  the 
germinating  dishes  were  also  covered  with  Valspar,  and  purified  salts 
were  used  for  the  solutions. 

Seventy-two  seedlings  of  each  group — all  of  the  group  without 
aluminum  which  were  large  enough — were  transferred  to  culture  jars. 
The  solutions  and  containers  were  of  the  same  kind  as  those  employed 
for  the  first  generation. 

After  being  transferred  to  the  final  solutions  the  plants  of  the 
group  with  aluminum  did  not  do  so  well  as  those  of  the  group  without 
it.  At  the  end  of  two  weeks  some  of  the  plants  of  the  group  without 
aluminum  were  larger  than  those  of  the  group  with  aluminum.     The 


Fig.   1.     Millet  seedlings. 

Left:   From  seed  grown  with  aluminum. 

Right:   From  seed  grown  without  aluminum. 

roots  of  most  of  the  plants  in  the  aluminum  group,  and  some  in  the 
group  without  aluminum,  appeared  to  be  infected  with  fungi  about 
the  end  of  the  sixth  week.  They  were  probably  infected  earlier  but 
not  to  an  extent  that  could  be  easily  noticed.  At  the  end  of  twelve 
weeks  some  of  the  plants  in  the  group  with  aluminum  were  dead. 
There  were,  however,  five  plants  with  large  heads,  which  appeared  to 
be  filling,  and  seven  plants  with  smaller  heads.  The  plants  with  the 
large  heads  were  correspondingly  large  plants,  and,  although  their 
roots  were  not  in  good  condition,  they  were  better  than  those  of  the 
other  plants  in  that  group.  In  the  group  without  aluminum  only  two 
small  heads  developed. 

In  spite  of  the  fact  that  the  plants  of  the  aluminum  group  were 
more  severely  injured  by  fungi,  they  produced  more  and  better  heads 
than  the  group  without ;  the  leaves  also  of  those  plants  not  too  badly 
injured  were  broader  and  more  normal  in  appearance. 


1926] 


Sommer:  Aluminum  and  Silicon  for  Plant   Growth 


69 


The  series  was  not  weighed  because  the  fungal  attack  was  too  severe 
to  allow  sufficient  growth  to  make  the  figures  significant. 

In  experiments  similar  to  the  foregoing  with  peas  and  millet,  the 
degree  of  stimulation  caused  by  aluminum  was  quite  different.  It  may 
be,  inasmuch  as  the  pea  has  a  much  larger  seed,  and  therefore  probably 
more  stored  aluminum,  that  it  may  need  less  additional  aluminum  for 
its  development.  The  fact  that  nearly  all  pea  plants  in  solutions 
without  aluminum  produced  viable  seeds  makes  it  appear  that  their 


Fig.  2.     Millet  seedlings. 

Left:   From  seed  grown  without  silicon. 

Eight:   From  seed  grown  with  silicon. 

need  was  more  nearly  supplied  than  that  of  the  millet,  rather  than 
that  1  p.p.m.  aluminum  was  insufficient.  It  would  therefore  be  neces- 
sary to  grow  several  generations  in  order  to  determine  whether  or 
not  this  element  is  essential  to  the  growth  of  peas. 

The  results  with  millet,  however,  suggest  very  strongly  that 
aluminum  is  essential  to  its  growth.  The  fact  that  three-fourths  of 
the  seeds  of  plants  grown  in  solutions  without  aluminum  came  from 
a  single  culture,  while  the  other  twenty-four  cultures  yielded  only  a 
very  small  amount,  makes  it  appear  quite  probable  that  the  good 
growth  of  this  culture  was  due  to  contamination  with  aluminum. 


70  University  of  California  Publications   in  Agricultural  Sciences      [Vol.  5 


Experiments  with  Silicon 

Rice  was  chosen  for  the  first  experiment  in  which  to  study  the  effect 
of  silicon  on  plant  growth  because  of  the  large  amount  of  this  element 
found  in  its  ash. 

The  culture  solution  was  made  up  as  follows: 

Per  liter 

KN03 78  gm. 

CaSO,  saturated  solution  400  e.c. 

MgHP04  saturated  solution 500  e.e. 

FeS04   Trace 

Silicon  was  added  in  the  form  of  H2SiO;i  jelly.  This  was  precipitated 
from  J.  G.  Baker  "C.  P."  Na2Si03,  with  H2S04,  and  washed  until 
the  washings  gave  no  test  for  the  sulphate  ion. 

Eight  cultures  of  four  plants  each  were  set  up  in  the  following 
solutions : 

Solution  Treatment  Remarks 

(a)  Culture  solution  None  Purified  salts 

(b)  Culture  solution  H2Si03  Purified  salts 

(c)  Culture  solution  H2Si03  Unpurified  salts 

After  being  soaked  and  the  hulls  removed,  the  seed  was  germinated 
on  paraffined  mosquito  netting.  The  seedlings  were  quite  variable  in 
size  and,  since  it  was  assumed  that  plants  growing  without  silicon 
would  be  the  smallest,  the  best  plants  were  chosen  for  this  group,  the 
next  best  for  purified  salts  with  silicon,  and  the  smallest  for  the 
unpurified  salts.  It  was  hoped  in  this  way  to  overcome  apparent 
improvement  with  silicon  which  might  be  due  to  variability.  The 
seedlings  were  transferred  to  the  culture  solutions  July  8. 

The  culture  solutions  for  this  series  were  removed  on  the  following 
dates:  September  1,  12,  and  23;  October  -4  and  23;  November  22  and 
January  4.  Solutions  of  the  original  strength  were  used  until  Novem- 
ber 22,  when  they  were  replaced  by  solutions  of  one-half  the  original 
strength. 

OBSERVATIONS 

July  22.  Plants  in  solutions  with  silicon  appeared  to  be  as  large  as  those  in 

solutions  without. 
September  11.  Some  leaves   of   the  plants  of  the   group   without    silicon    were 

beginning  to  dry. 
September  23.  The  number  of  dry  leaves  of  plants  of  the  group  without  silicon 

was  increasing  rather  rapidly.    There  were  but  few  dry  leaves  on  plants 

of  the  other  two  groups.     Leaves  of  the  group  without  silicon  appeared 

quite  mottled. 


1926]  Sommer:  Aluminum  and  Silicon  for  Plant   Growth  71 

October  13.  Guttation,  which  had  been  quite  profuse  for  all  plants  from  the 
beginning,  had  ceased  in  the  group  without  silicon.  It  was  still  profuse 
on  plants  of  the  other  two  groups. 

October  19.  There  was  a  marked  decrease  in  the  amount  of  guttation  in  the 
groups  with  silicon.  Heads  were  beginning  to  develop  in  most  cultures; 
there  were  fewest  in  the  group  without  silicon. 

November  13.  Heads  in  the  group  without  silicon  were  developing  very  slowly. 
Plants  in  the  three  groups  appeared  very  different  in  size.  The  plants 
of  the  group  without  silicon  were  much  the  smaller  and  plants  of  the 
group  in  solutions  of  purified  salts  with  silicon  were  smaller  than  those 
in  solutions  of  unpurified  salts  with  silicon.  An  exudate  appearing  like 
crystals,  but  really  a  viscous  liquid,  had  formed  on  many  leaves  of  the 
plants  without  silicon. 

December  28.  Heads  of  plants  grown  with  silicon  were  much  larger  than  those 
of  the  group  without  and  appeared  to  be  filling.  A  few  leaves  of  the 
group  in  solutions  of  purified  salts  with  silicon  had  the  exudate  noted 
above  for  the  group  without  silicon. 

February  10.  Plants  harvested. 

No  seed  matured  in  any  of  the  cultures. 

The  roots  of  plants  of  the  group  without  silicon  were  in  poor  condi- 
tion and  beginning  to  disintegrate.  The  roots  of  the  two  other  groups 
were  in  good  condition. 

The  roots  were  matted  together,  so  were  weighed  per  culture 
(groups  of  four)  and  averaged.  The  average  weights  of  roots  and 
tops  are  given  in  table  3. 

TABLE  3 

Average  Dry  Weight  in  Grams  of  Bice  Plants  Grown  With  and  Without 

Silicon 

Solution  No.  of  plants  Tops  Roots 

(a)  Purified  salts    32  3.29  ±  .34  1.1 

(b)  Purified  salts  +  Si  32  5.33  ±  .37  1.7 

(c)  Unpurified  salts  +  Si 32  6.58  ±  .45  2.1 

The  weights  of  the  plants  with  silicon  were  greater  than  those  of 
the  plants  without.  In  this  case  as  in  the  aluminum  series  with  peas, 
the  unpurified  salts  gave  the  best  growth,  which  indicates  that  the 
purified  salts  lacked  not  only  the  element  to  be  studied,  but  one  or 
more  other  elements  not  usually  considered  essential  but  which  must 
play  some  role  in  plant  nutrition. 


72  University  of  California  Publications  in  Agricultural  Sciences      [Vol.  5 


Silicon  Series  with  Millet 

Liberty  millet  was  the  variety  employed  for  this  experiment.  It 
was  afterward  learned  that  it  often  gives  a  very  poor  yield  of  grain 
under  field  conditions. 

The  culture  solution  used  was  the  same  as  that  of  the  preceding 
series  except  that  2  p. p.m.  of  manganese  in  the  form  of  MnS04  was 
added. 

Two  groups  of  plants,  one  in  solutions  of  purified  salts,  and  the 
other  in  solutions  of  purified  salts  with  silicon,  were  included  in  this 
series.     Each  group  included  30  cultures  of  -i  plants  each. 

Two-quart  mason  jars  were  employed  as  containers. 

The  seed  was  germinated  on  mosquito  netting  and  the  seedlings 
transferred  to  the  culture  solutions  March  29. 

The  plants  grew  rapidly  and  were  beginning  to  head  out  April  10. 
Little  difference  could  be  noticed  in  the  appearance  of  the  two  groups. 
The  plants  of  the  group  with  silicon  appeared  to  be  somewhat  better. 

Plants  were  harvested  June  26. 

All  plants  had  heavy  short  roots  with  many  fine  short  laterals. 
The  roots  of  the  plants  with  silicon  had  more  fine  laterals  and  were 
on  the  average  about  an  inch  longer  than  those  without.  There  was 
little  difference  in  the  dry  weights  of  the  two  groups.  The  yield  of 
seed  was  very  small,  23  seeds  for  plants  grown  without  silicon,  and  126 
for  plants  grown  with  silicon.  The  seeds  from  the  two  groups  of 
plants  were  quite  different  in  appearance.  Those  grown  with  silicon 
were  much  more  glossy  and  lighter  in  color. 

The  average  weight  per  plant  is  given  below : 

Dry  Weight  of  Millet  Plants  in  Grams  (Average  per  Plant) 
No.  of  plants  Tops  Roots 

With  Si  120  3.1  ±  1.7  1.85  ±  .37 

Without  Si  120  2.5  ±  1.1  1.6    ±  .37 

The  difference  in  weight  in  this  series  is  not  large  enough  to  be  signi- 
ficant. The  absolute  difference  in  the  number  of  seeds  is  large,  but 
the  total  yield  is  too  small  to  be  of  value. 


1926]  Sommer:  Aluminum  and  Silicon  for  Plant  Growth  73 


Second  Generation  Series 

The  seeds  of  the  plants  grown  in  the  preceding  experiment  were 
used  for  a  second  generation  series.  All  of  the  seeds  of  the  group 
grown  without  silicon  and  an  equal  number  grown  with  silicon  were 
used.  All  of  the  seeds  from  the  group  grown  with  silicon,  and  most 
of  the  seeds  of  the  group  grown  without  silicon,  germinated. 

At  the  end  of  the  first  week  after  germination  the  seedlings  of  the 
group  with  silicon  were  larger  than  those  of  the  group  without.  The 
plants  were  destroyed  by  mice  before  they  could  be  transferred  to  the 
culture  jars. 

Second  Millet  Series 

The  culture  solutions  and  the  kind  of  millet  seed  used  Avere  the 
same  as  those  of  the  preceding  series. 

Large  containers  of  16-liter  capacity  were  employed.  There  were 
2  cultures  of  24  plants  each,  in  each  group.  This  series  was  transferred 
to  the  culture  solutions  September  28  and  harvested  January  7. 

TABLE  4 
Description  of  Millet  Plants  Grown  With  and  Without  Silicon 

With  Si  Without  Si 

(48  plants)  (48  plants) 

Length  of  roots  in  cm 24  ±  4  31  ±  4 

Lengths  of  tops  in  em 52  ±  7  44  ±  6 

Dry  weight  of  tops  in  gm 44  ±  .09  .29  ±  .07 

Total  dry  weight  in  gm 45  ±  .11  .38  ±  .07 

Weight  of  seed  per  plant  in  gm 13  ±  .04  .07  ±  .03 

The  plants  of  this  series  were  very  different  in  size  and  general 
appearance  from  those  grown  in  the  spring.  They  did  not  have  as  tall 
rigid  stalks  and  the  roots  were  much  longer  and  finer.  There  were 
fewer  roots  from  the  crown  and  the  laterals  were  very  much  longer. 
The  plants  were  very  variable  in  size. 

There  was  a  large  difference  in  the  yield  of  seeds  with  the  same 
difference  in  appearance  as  was  noted  for  the  first  series.  The  total 
weight  of  seeds  for  the  group  grown  with  silicon  with  6.14  grams  and 
that  without  silicon  was  3.39  grams. 

One  of  the  two  containers  without  silicon  had  larger  plants  with 
more  seed  than  the  other. 

The  average  weights  per  plant  and  length  of  roots  are  given  in 
table  4  above. 


74  University  of  California  Publications  in  Agricultural  Sciences      [Vol.  5 

Since  the  plants  in  one  container  without  silicon  were  much  larger 
than  those  in  the  other,  it  was  thought  well  to  get  the  averages  for 
each  container  as  these  differences  may  have  been  due  to  contamination 
by  dust.    The  values  are  given  in  table  5. 

TABLE  5 
Description  of  Millet  Plants  Grown  Without  Silicon 

Container  I  Container  II 

Length  of  roots  in  cm 34  ±  4  27  ±  4 

Length  of  tops  in  cm 47  ±  6  41  ±  6 

Dry  weight  of  tops  in  gm 33  ±  .06  .25  ±  .06 

Total  dry  weight  in  gm 43  ±  .08  .33  ±  .06 

Weight  of  seed  per  plant  in  gm 09  ±  .04  .06  ±  .03 

In  the  preceding  series  the  roots  of  the  plants  grown  with  silicon 
were  longer  and  heavier  than  those  grown  without.  In  this  series  the 
reverse  was  true.  There  was,  however,  sufficient  increase  in  the  dry 
weight  of  the  tops  for  the  plants  grown  with  silicon  to  make  the  total 
dry  weight  greater  than  that  of  plants  grown  without  silicon.  The 
yield  of  seeds  in  this  series  was  much  larger  and,  since  the  plants  with 
silicon  produced  nearly  twice  as  much  weight  of  seeds  as  the  plants 
without  silicon,  this  difference  may  be  considered  significant. 


Second  Generation  Millet  Series  With  and  Without  Silicon 

Two  hundred  seeds  of  each  group  of  the  preceding  series  were  used 
for  a  second  generation  experiment. 

The  netting  and  the  germinating  dish  were  covered  with  Valspar, 
and  purified  salts  were  used  in  making  up  the  solution. 

The  seed  of  the  plants  grown  without  siliqon  germinated  very 
poorly  and  in  a  few  days  were  so  covered  with  mold  that  they  had 
to  be  discarded.  There  was  100  per  cent  germination  of  the  seed  of  the 
plants  grown  with  silicon,  and,  although  they  were  germinated  on  the 
same  piece  of  netting  as  the  seed  from  plants  grown  without  silicon, 
they  were  free  from  mold. 

A  second  lot  of  seed,  three  hundred  of  each  group,  were  treated 
with  1-5000  HgCl2  solution  for  three  minutes,  washed  with  sterile 
distilled  water,  and  germinated  under  sterile  conditions.  The  con- 
tainer, netting,  and  solution  were  sterilized  and  kept  under  a  sterile 
bell  jar.  For  the  first  four  days  no  growth  of  fungi  could  be  noticed, 
and  the  germination  of  the  seeds  from  the  plants  grown  with  silicon 
was  excellent,  while  that  from  the  silicon-free  group  was  poor.    After 


1926]  Sommer:  Aluminum  and  Silicon  for  Plant  Growth  75 

the  fourth  day  a  slight  growth  of  mold  could  be  seen  on  the  seeds  of 
the  silicon-free  group.  This  mold  grew  rapidly  but  did  not  attack 
the  seed  of  the  group  grown  in  the  presence  of  silicon. 

The  results  of  germination  are  as  follows;  all  but  two  seeds  of  the 
group  grown  with  silicon  germinated : 

Silicon-free  Group 

No  signs  of  germination  49 

Very  feeble — dead  at  time  of  transplanting 103 

Very  small  plants — no  roots  39 

Very  small  plants — small  roots 34 

Hardly  large  enough  to  plant  41 

Fair  size   30 

Nearly  as  large  as  those  with  silicon  4 

The  seedlings  are  shown  in  figure  2. 

Most  of  the  larger  plants  of  the  silicon-free  group  were  from  seeds 
which  came  from  the  culture  of  the  preceding  series,  which  had  pro- 
duced the  largest  plants.  One  hundred  and  fifty  seeds  from  each 
culture  were  used.  The  seeds  from  the  two  cultures  were  kept  separate 
during  germination.  This  is  not  shown  by  the  picture  because  the 
line  dividing  them  is  at  right  angles  to  the  line  separating  the  two 
groups ;  that  is,  the  seed  from  the  plants  grown  with  and  without 
silicon. 

Seventy-five  plants  of  each  group  were  transferred  on  April  28  to 
jars  like  those  used  in  the  preceding  series.  There  were  twenty-five 
plants  to  each  jar. 

OBSEEVATIONS 

May  8.  Seven  plants  in  the  silicon-free  series  were  dead. 

May  15.  The  plants  in  two  of  the  jars  with  silicon  appeared  less  green  and 
somewhat  smaller  than  those  of  the  other  jar  in  that  group.  Examination 
showed  their  roots  to  be  attacked  by  aphis.  The  covers  of  all  jars  were 
raised  and  "nicofume, "  an  insecticide,  was  burned. 

May  29.  Aphids  were  on  the  roots  of  most  of  the  plants.    Nicofume  was  burned. 

June  2.  Most  of  the  plants  in  two  of  the  cultures  of  the  group  with  silicon,  and 
a  few  of  the  plants  in  two  of  the  cultures  without  silicon,  had  heads. 

June  15.  Most  of  the  plants  in  all  cultures  except  one  in  the  group  with  silicon 
had  heads.  The  heads  of  the  plants  in  this  culture  appeared  to  have  been 
injured  when  they  were  beginning  to  form.  Small  dry  rudimentary  heads 
were  all  that  could  be  seen  and  they  were  present  on  all  plants  of  this 
culture. 

July  6.  Aphis  found  on  the  roots  and  tops  of  most  of  the  plants.  Nicofume 
was  burned. 

July  21.  The  plants  were  harvested. 


76  University  of  California  Publications  in  Agricultural  Sciences      [Vol.5 

One  culture  in  the  silicon-free  group  had  only  2  seeds,  another 
had  68,  and  the  third  had  none ;  the  total  weight  was  0.37  grams.  The 
weight  of  seed  from  the  two  cultures  of  the  group  with  silicon  which 
produced  heads  was  3.92  grams.  The  roots  and  tops  were  not  weighed 
separately  since  some  of  the  plants  had  slipped  rather  far  down  into 
the  solution  and  had  roots  high  up  on  the  stalks.  The  average  weight 
of  plants  grown  with  silicon  was  2.1  ±  0.5  grams,  that  of  plants 
without  was  1.7  ±  0.8  grams. 

The  type  of  plant,  with  the  exception  of  the  plants  in  one  of  the 
jars  without  silicon  (the  jar  to  which  the  smallest  seedlings  had  been 
transferred  and  where  seven  of  the  plants  had  died),  was  the  same 
as  that  of  the  plants  grown  during  the  preceding  spring.  Those  of 
the  exceptional  culture  had  roots  like  the  plants  grown  in  the  fall  and 
the  tops  were  of  an  intermediate  type.  There  was  great  variability  in 
the  size  of  the  plants,  especially  with  those  grown  without  silicon. 

The  kind  of  differences  for  the  second  generation  was  the  same 
as  that  for  the  first  generation ;  that  is,  there  was  but  little  difference 
in  dry  weight  between  the  groups  with  and  without  silicon,  but  a  great 
difference  in  the  yield  of  seed.  The  difference  in  the  yield  of  seed  was 
much  greater  in  the  second  generation. 


Silicon  Series  with  Penisitum  vilosum 

This  plant  was  chosen  because  of  the  high  silicon  content  of  its 
leaves.  An  analysis  showed  an  ash  content  of  13  per  cent,  75  per  cent 
of  which  was  Si02. 

The  solution  used  was  the  same  as  that  in  the  preceding  series. 
One  hundred  plants  were  included  in  each  group,  one  with  and  one 
without  silicon,  and  two-quart  mason  jars  were  employed  as  containers. 
There  were  four  plants  per  jar. 

The  plants  were  transferred  to  the  culture  solutions  February  21. 
They  showed  no  signs  of  head  production  when  they  were  harvested 
July  20. 


1926 J  Sommer:  Aluminum  and  Silicon  for  Plant   Growth  77 


OBSERVATIONS 

At  the  end  of  five  weeks  the  plants  grown  with  silicon  were  larger 
and  greener  than  those  grown  without  it.  The  leaves  of  those  without 
silicon  appeared  mottled  like  those  of  the  corresponding  group  of  rice. 
By  the  time  the  plants  had  been  transplanted  eight  weeks,  they  had  so 
many  tillers  that  part  of  the  cork  had  to  be  cut  away.  Soon  after  this 
the  plants  in  the  silicon-free  solutions  began  to  grow  rapidly  and  at 
the  time  of  harvest  appeared  about  as  large  as  those  grown  with  silicon. 
The  leaves,  however,  were  not  so  green.  The  leaves  of  the  plants  grown 
without  silicon  were  much  smoother  than  those  grown  with  silicon. 
There  was  a  tremendous  variability  in  the  size  of  the  plants  but  the 
variability  was  much  less  by  culture.  The  average  weights  are  there- 
fore reported  as  total  dry  weight  per  culture  and  are :  with  silicon 
30.8  ±  2.6  grams;  without  silicon  29  ±  1.8  grams. 

The  average  for  the  plants  without  silicon  does  not  include  one 
culture  which  was  very  much  smaller  than  the  others. 

These  results  with  Penisitum  vilosum  are  inconclusive,  since  there 
was  for  a  while  a  marked  difference  in  the  apparent  size  of  the  plants 
of  the  two  groups,  which  disappeared  later  on.  This  change  was  prob- 
ably due  to  contamination,  since  it  was  impossible  to  shut  out  dust 
entirely — especially  after  part  of  the  cork  had  been  cut  away. 

In  experiments  with  and  without  silicon,  rice  and  Golden  millet 
(that  used  in  the  aluminum  series),  showed  very  marked  differences  in 
dry  weight ;  the  increase  when  silicon  was  added  being  60  per  cent  for 
the  tops  of  rice  and  50  per  cent  for  the  tops  of  millet.  Liberty  millet, 
on  the  other  hand,  showed  no  marked  differences  in  dry  weight,  but 
the  increase  in  yield  of  grain  through  the  addition  of  silicon  was  large, 
especially  in  the  second  generation  experiment,  indicating  that  silicon 
may  be  essential  to  its  growth,  but  that  either  the  conditions  under 
which  it  grew,  in  these  experiments,  were  not  sufficiently  controlled, 
or  that  enough  silicon  is  stored  in  the  seed  to  carry  the  plants  through 
at  least  two  generations. 


78  University  of  California  Publications  in  Agricultural  Sciences      [Vol.  5 


DISCUSSION 

Until  recently  the  importance  of  small  amounts  of  elements,  other 
than  iron,  has  received  practically  no  attention.  Bertrand  had  stressed 
the  importance  of  manganese,  but  it  remained  for  McHargue9  to  prove 
it  to  be  essential.  The  work  of  Maze,8  indicating  that  there  may  be  a 
considerable  number  of  elements  necessary  in  very  small  quantities, 
may  explain  why  culture  solutions  made  up  with  unpurified  salts,  when 
included  in  the  series  reported  in  this  paper,  gave  the  best  yields. 
The  results  of  Warington17  with,  boron  suggest  that  plants  may  differ 
in  their  requirements  for  ions.  This  was  brought  out  accidentally 
by  the  writer  in  an  attempt  to  grow  Yicia  faba  with  and  without 
aluminum.  The  same  salts  were  used  as  had  been  used  for  millet,  but 
the  beans  grew  only  for  a  short  time  and  showed  the  symptoms 
described  by  Warington,  for  boron-starved  plants.  Although  they  had 
ceased  growing  and  were  in  very  poor  condition,  the  addition  of 
y-2  p. p.m.  boron  caused  excellent  new  growth  of  both  tops  and  roots. 

The  difference  in  the  needs  of  different  plants  may,  however,  be 
one  of  amount  rather  than  of  kind  of  elements.  The  amount  of  certain 
elements  needed  for  some  plants  may  be  so  small  that  sufficient  puri- 
fication of  salts  vised  in  relatively  large  amounts  may  be  practically 
impossible.  Stoklasa's10  work  with  hydrophytes,  in  which  some  of  the 
plants  failed  to  grow  without  the  addition  of  aluminum,  and  the  work 
of  the  writer  with  peas  and  millet,  seem  to  bear  out  this  idea.  This 
seems  also  to  be  shown  in  the  silicon  experiments  when  we  compare 
the  results  of  Kreuzhage  and  Wolff"  with  oats,  and  of  the  writer  with 
millet,  with  the  results  obtained  by  the  writer  with  rice.  The  signi- 
ficant results  with  oats  and  millet  were  chiefly  concerned  with  seed 
production,  while  with  rice  there  was  a  very  large  difference  in  dry 
weight. 


1926]  Sommer:  Aluminum  and  Silicon  for  Plant  Growth  79 


SUMMARY  AND  CONCLUSIONS 

Experiments  were  conducted  to  determine  whether  or  not  aluminum 
and  silicon  are  essential  to  plant  growth.  Especially  purified  salts 
and  redistilled  water  were  used  for  culture  solutions.  All  containers 
were  coated  to  prevent  solution  of  the  glass. 

The  addition  of  aluminum  to  culture  solutions  in  which  peas  were 
grown  gave  only  a  small  increase  in  total  dry  weight  but  a  somewhat 
greater  increase  in  the  amount  of  seed. 

The  addition  of  aluminum  to  culture  solutions  in  which  millet  was 
grown  gave  a  marked  increase  in  growth ;  the  increase  in  the  amount 
of  seed  being  very  great.  The  results  of  this  experiment  strongly 
indicate  that  aluminum  is  essential  to  the  normal  development  of 
millet. 

Attempts  to  grow  a  second  generation  of  peas  and  millet  were 
unsuccessful,  but  seedlings  from  seeds  grown  with  aluminum  were 
much  better  than  those  from  seeds  grown  without  it.  The  germination 
also,  in  the  case  of  millet,  was  better  with  the  seeds  from  plants  grown 
with  aluminum. 

The  improvement  in  the  growth  of  rice  on  the  addition  of  silicon 
was  great  enough  to  indicate  that  silicon  is  essential  to  its  growth. 

The  addition  of  silicon  to  culture  solutions  in  which  millet  was 
grown  gave  marked  increases  in  seed  production  and,  in  one  series,  a 
marked  increase  in  both  seeds  and  dry  weight. 

In  a  second  generation  series  with  millet,  grown  with  and  without 
silicon,  the  difference  in  dry  weight  was  very  slight  but  the  yield  of 
seed  for  plants  grown  with  silicon  was  more  than  ten  times  as  great 
as  that  for  plants  grown  without  it. 

Seeds  of  millet  grown  without  silicon  were  badly  infected  by  fungi 
while  those  grown  wTith  silicon  were  not  attacked. 

An  experiment  with  and  without  silicon  in  which  Penisitum  vilosum 
was  used  was  inconclusive,  since  the  marked  differences  which  appeared 
after  the  first  month  disappeared  later  on.  The  change  may  have  been 
due  to  contamination  by  dust. 


80  University  of  California  Publications  in  Agricultural  Sciences      [Vol.  5 


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UNIVERSITY  OF  CALIFORNIA  PUBLICATIONS—  (Continued) 

BOTANY. — W.  A.  Setchell  and  R.  C.  Holman,  Editors.  Volumes  I-IV  $8.50  per  volume; 
volume  V  and  following  $5.00  per  volume.  Volumes  I  (pp.  418),  II  (pp.  360), 
m  (pp.  400),  IV  (pp.  397),  V  (pp.  589),  VI  (pp.  517),  VII  (pp.  506),  IX 
(pp.  423),  and  X  (pp.  437),  completed.  Volumes  VIII,  XI,  XII,  and  "Errr  ta 
progress. 

VoL  8.  1.  The  Marine  Algae  of  the  Pacific  Coast  of  North  America.  Part  I.  Myxo- 
phyceae,  by  William  Albert  Setchell  and  Nathaniel  Lyon  Gardner.  Pp. 
1-188,  plates  1-8.    November,  1919 .. 1.60 

2.  (The  same.)     Part  n.  Chlorophyceae,  by  William  Albert  Setchell  and 

Nathaniel  Lyon  Gardner.    Pp.  139-374,  plates  9-33.    July,  1920 _    2.78 

3.  (The  same.)     Part  n.  Melanophyceae.  Pp.  383-898,  plates  34-107.    June, 

1925 _ 5.00 

VoL  9.    A  Report  upon  the  Boreal  Flora  of  the  Sierra  Nevada  of  California,  by  Frank 

Jason  Smiley.    423  pages,  7  plates.    October,  1921 . 6.00 

VoL  10.   1.  The  Genus  Fucus  on  the  Pacific  Coast  of  North  America,  by  Nathaniel 

Lyon  Gardner.    Pp.  1-180,  pis.  1-60.    AprU,  1922 2.25 

2.  Plantae   Mexicanae   Purpusianae,   XI,   by   Townshend   Stith  Brandegee. 

Pp.  181-188.     November,  1922 _ _ .15 

3.  A  Revision  of  the  Californlan  Species  of  Lotus,   by  Alice  M.   Ottley. 

Pp.  189-305,  plates  61-82,  10  maps.    August,  1923 2.00 

4.  Notes  on  a  Collection  of  New  Zealand  Hepatdcae,  by  William  Henry  Pear- 

son.   Pp.  307-370,  plates  83-103. 

5.  More  New  Zealand  Hepaticae,  by  William  Henry  Pearson.    Pp.  373-392, 

plates  104-109. 

Nos.  4  and  5  in  one  cover.    June,  1923 _ L26 

6.  Parasitic  Florideae  n,  by  William  Albert  SetchelL    Pp.  393-396. 

7.  A  Revision  of  the  West  North  American  Species  of  Callophyllis,  by 

William  Albert  SetchelL    Pp.  397-401. 

Nos.  6  and  7  in  one  cover.    May,  1923 „ .26 

8.  Plantae  Mexicanae  Purpusianae,  by  Townshend  Stith  Brandegee.  Pp. 
403-421.     September,  1924 25 

9.  New  Species  of  Plants  from  Indo-China,  by  Elmer  D.  Merrill.  Pp.  423- 
430.    October,  1924 „ _ 25 

Vol.  11.  1.  Interspecific  Hybridization  in  Nicotiana.  On  the  Results  of  Backcrossing 
the  F,  Sylvestris-Tabacum  Hybrids  to  Sylvestris,  by  Thomas  Harper 
Goodspeed  and  Roy  Elwood  Clausen.  Pp.  1-30,  12  figures  in  text. 
August,  1922    _ „ _.      .40 

2.  Inheritance  in  Nicotiana  Tabacum.  VI.  A  Mendelian  Analysis  of  Certain 
Flower  Form,  Flower  and  Filament  Color,  and  Leaf-base  Characters,  by 
M.  A.  Kelaney.    Pp.  31-59,  6  figures  in  text.    August,  1925 25 

VoL  12.   1.  Lichenes  a  W.  A.  Setchell  et  H  E.  Parks  in  Insula  Tahiti  a  1922  Collect!, 

scripsit  Edv.  A.  Vainio.    Pp.  1-16,  January,  1924 35 

2.  Report  upon  a  Collection  of  Ferns  from  Tahiti,  by  William  A.  Maxon. 

Pp.  17-44,  plates  1-6.    May,  1924 z _ .45 

3.  Tahitian  Mosses,  Collected  by  W.  A.  Setchell  and  H.  E.  Parks,  Determined 

by  V.  F.  Brotherus.    Pp.  45-48.    September,  1924 —      .25 

Vol.  13.  1  Phycological  Contributions.   VII,  by  W.  A.  Setchell  and  N.  L.  Gardner. 

Pp.  1-13.    October,  1924 25 

2.  Hemitonia  congesta.    A  Genetic  Ecologic  and  Taxonomic  Study  of  the  Hay- 

field  Tarweeds,  by  Ernest  Brown  Babcock  and  Margaret  Mann  Lesley. 

Pp.  15-100,  7  plates,  4  figures  in  text.    December,  1924 1.35 

3.  Contributions  Toward  a  Knowledge  of  the  Life-histories  of  the  Melano- 
phyceae. A  Preliminary  Report,  by  Margaret  Esther  Myers.  Pp.  109- 
124,  plates  8-10. 

4.  Notes  on  Microdictyon,  by  William  A.  Setchell.    Pp.  101-107. 
Nos.  3  and  4  in  one  cover.    September,  1925 25 

5.  Observations  on  the  Origin  of  Secondary  Dormant  Buds  in  Deciduous  Fruit 
Trees,  by  Bruno  Hahne.    Pp.  125-128,  plate  11.    January,  1926 25 


